1. Field of the Invention
The present invention relates to an electron emission device, and more particularly to such a device having an electron emission electrode with a pointed end and an electrode positioned opposite to said pointed end.
2. Related Background Art
As an electron source there has been utilized thermal electron emission from a thermal cathode. Such an electron emission utilizing a thermal cathode has been associated with the drawbacks of a large energy loss in heating, necessity of heating means, a considerable time required for preparatory heating, and the tendency of instability of the system caused by heat.
For these reasons there have been developed electron emission devices not relying on heating, among which there is known an electron emission device of field effect (FE) type.
FIG. 1 is a schematic view of a conventional electron emission device of field effect type.
As shown in FIG. 1, the conventional electron emission device of field effect type is composed of a cathode chip 20 formed on a substrate 23 and having a sharply pointed end for obtaining a strong electric field, and an attracting electrode 22 formed on the substrate 23 across an insulating layer 21 and having an approximately circular aperture around the pointed end of the cathode chip 20, wherein a voltage is applied across said cathode chip 20 and said attracting electrode 22 with the positive side at the latter, thereby causing electron emission from the pointed end of the cathode chip 20 where the intensity of electric field is larger.
However, in such a conventional field effect electron emission device, the sharp pointed end of the cathode chip 20 is difficult to make, and has been generally manufactured by electrolytic polishing followed by remolding. This process is however cumbersome, requiring many working steps, and is difficult to automate as it involves various empirical factors. Consequently the manufacturing conditions fluctuate easily, and the product quality cannot be made constant. Also the laminate structure tends to result in a registration error between the cathode chip and the attracting electrode 22.
In consideration of the foregoing, the object of the present invention is to provide a field effect electron emission device capable of simplifying the manufacturing process of the pointed end of the electron emitting cathode, and being formed as a thin structure.
The above-mentioned object can be achieved, according to an embodiment of the present invention, by an electron emission device having an electron emission electrode with a pointed end and a counter electrode positioned opposite to said pointed end, both formed by fine working of a conductive layer laminated on an insulating substrate.
The intensity of the electric field generally required for electron emission is 108 V/cm or higher, and, in the presence of such electric field, the electrons in the solid substance pass through a potential barrier at the surface by tunnel effect, thus causing electron emission.
When a voltage E is applied between the electron emission electrode and the counter electrode, and the radius r of curvature of an electron emitting portion of the electron emission electrode is small, the intensity of electric field E at said electron emitting portion satisfies a relation:   E  ∝      V    r  
In the electron emission, the range of energy of emitted electrons should preferably be made small in order to improve the convergence of the electrons, and the device is preferably drivable with a low voltage. For these reasons said radius r of curvature should preferably be made as small as possible.
Also in order to stabilize the electron emission voltage, it is desirable to precisely control the distance between the electron emission electrode and the counter electrode.
The present embodiment minimizes the radius of curvature of the electron emission electrode and precisely controls the distance between said electron emission electrode and the counter electrode, utilizing fine working technology.
In another embodiment of the present invention, the above-mentioned object can be achieved by an electron emission device provided with an electron emission electrode having a pointed end on an insulating substrate in such a manner as to be substantially parallel to said substrate, and an attracting electrode positioned opposite to said pointed end and having an electron emission aperture.
In the present embodiment, an electron emission electrode having a pointed end and an attracting electrode positioned opposite to said pointed end and having an electron emission aperture are formed substantially parallel to the surface of an insulating substrate, and a voltage is applied across said electron emission electrode and said attracting electrode, with the positive side at the latter, to cause electron emission from said pointed end through said electron emission aperture substantially parallel to the surface of said insulating substrate.